Silicon carbide body and method of forming same

ABSTRACT

A method of forming a ceramic article including providing a ceramic body comprising silicon carbide, and treating the ceramic body in an atmosphere comprising an oxidizing material to remove a portion of the ceramic body through a chemical reaction between a portion of the ceramic body and the oxidizing material.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(e) to U.S. PatentApplication No. 61/428,289 entitled “Silicon Carbide Body and Method ofForming Same,” by Reilly et al., filed Dec. 30, 2010, which is assignedto the current assignee hereof and incorporated herein by reference inits entirety.

BACKGROUND

1. Field of the Disclosure

The following is directed to a method of forming a ceramic article, andparticularly, a method of forming a silicon carbide body.

2. Description of the Related Art

Silicon carbide-based ceramic materials are utilized in manyapplications for their refractory properties and mechanical properties.Among the types of silicon carbide-based ceramics available, varioustypes exist based on the particular forming process, including forexample, sintered silicon carbide, hot pressed silicon carbide, andrecrystallized silicon carbide. Each of the various types of siliconcarbide bodies can have distinct features. For example, sintered siliconcarbide (such as Hexyloy®) can be a very dense material, but isgenerally expensive and complex to produce. On the other hand, more costeffective but relatively porous silicon carbide materials such asnitride-bonded silicon carbide (known by acronyms such as NBSC and NSIC)have found practical use in refractory applications. Such refractorycomponents include furnace or kiln furniture utilized in connection withholding or supporting work pieces during firing operations, as well asrefractory lining materials and structural walls defining the furnaceheating area.

However, certain process limitations still exist for certain siliconcarbide bodies. In particular reference to nitride-bonded siliconcarbide, during formation of the body, fibers of silicon nitride areformed on the surface body. Such fibers can roughen the surface, limitthe ability to conduct post-forming processes, and change the appearanceof the body, which may be unsuitable for a customer's intended use.Accordingly, it is common in the industry to remove the silicon nitridefibers from the material prior to further processing. The fibers areremoved through physical techniques, such as sandblasting the surface ofthe silicon carbide body. Such processes are time consuming and oftenlimited in efficacy.

SUMMARY

According to one aspect, a method of forming a ceramic article includesproviding a ceramic body comprising silicon carbide, and treating theceramic body in an atmosphere comprising an oxidizing material to removea portion of the ceramic body through a chemical reaction between aportion of the ceramic body and the oxidizing material.

In another aspect, a method of forming a ceramic article includesproviding a ceramic body comprising a fibrous material overlying anexterior surface of the ceramic body and treating the ceramic body witha gaseous reactant material to remove the fibrous material from theceramic body through a chemical reaction between the gaseous reactantmaterial and the fibrous material.

Yet another aspect includes a method of forming a ceramic articlecomprising firing a ceramic body comprising silicon carbide in a firstatmosphere and treating the ceramic body in a second atmosphere afterfiring, wherein the second atmosphere is different than the firstatmosphere and comprises a reactant material that chemically reacts withthe ceramic body and removes a portion of the ceramic body.

In still another aspect, a body includes nitride-bonded silicon carbide,wherein the body comprises pores at an exterior surface and a majorityof the pores are defined by smooth, non-fibrous surfaces when viewed ata magnification of at least 1000× for at least 2 random locations acrossthe exterior surface of the body.

According to one aspect, a ceramic article includes a body havingnitrogen-bonded silicon carbide having a non-fibrous exterior surface,wherein a non-fibrous exterior surface is defined by a surface havingnot greater than 10 fibers per 100 square microns at a magnification ofat least 1000× for at least 2 random locations across the exteriorsurface of the body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 includes a flow chart describing a process for forming a ceramicarticle in accordance with an embodiment.

FIG. 2 includes a firing schedule of temperature versus hours for aceramic body formed according to an embodiment.

FIG. 3 includes a magnified image of a portion of a ceramic body inaccordance with an embodiment.

FIG. 4 includes a magnified image of a portion of a ceramic body inaccordance with an embodiment.

FIG. 5 includes a magnified image of a portion of a conventional ceramicbody.

FIG. 6 includes a magnified image of a portion of a conventional ceramicbody.

DETAILED DESCRIPTION

The following is directed to ceramic articles comprising silicon carbideand methods of forming such articles. More particularly, the followingis directed to refractory bodies incorporating silicon carbide, and caninclude nitride-bonded silicon carbide compositions. Reference herein tonitride-bonded silicon carbide can include ceramic bodies that have amajority content of silicon carbide. The bodies can also include somecontent of other materials including nitrides, oxides, carbides,silicon, oxynitrides, and a combination thereof.

In reference to the method of forming a ceramic article in accordancewith an embodiment, FIG. 1 provides a flow chart illustrating a processof forming such articles. As illustrated, the process of forming aceramic article can be initiated by forming a mixture at step 101. Themixture can include a combination of powder components which may bemixed together in a dry form. Alternatively, the mixture may be in theform of a slurry, including a liquid vehicle containing a mixture ofpowder material.

The process of forming a mixture can include blending fine and coarsesilicon carbide powder materials together. The fine silicon carbidepowder can have an average particle size that is less than an averageparticle size of the coarse silicon carbide powder. The difference inthe average particle size between the fine and the coarse siliconcarbide powders can be at least about 10% based on the larger of the twoparticles. The mixture can include a bimodal distribution of siliconcarbide powder material, such that upon analysis of the mixture, twodistinct modes defined by the distinct fine and coarse particle sizesare evident. Other mixtures can include more than two modes, such thatthe mixture can include a trimodal mixture of silicon carbide powders.

For example, the coarse silicon carbide particles can have an averageparticle size of at least about 40 microns, at least about 50 microns,at least about 60 microns, at least about 70 microns, or even at leastabout 80 microns. Still, the coarse silicon carbide particles can havean average particle size that is not greater than about 2500 microns,such as less than about 2000 microns, less than about 1500 microns, lessthan about 1000 microns, less than about 800 microns, less than about500 microns, or even less than about 250 microns. The coarse siliconcarbide powder can have an average particle size within a range betweenany of the minimum and maximum values noted above.

The fine silicon carbide powder can have an average particle size thatis significantly less than the average particle size of the coarsesilicon carbide powder. For example, the fine silicon carbide particlescan have an average particle size of not greater than about 30 microns,such as not greater than about 25 microns, not greater than about 20microns, not greater than about 15 microns, or even not greater thanabout 10 microns. Still, the fine silicon carbide particles can have anaverage particle size that is at least about 0.01 microns, such as atleast about 0.05 microns, at least about 0.1 microns, or even at leastabout 0.5 microns. The fine silicon carbide powder can have an averageparticle size within a range between any of the minimum and maximumvalues noted above.

The mixture can include a blend of fine and coarse silicon carbidepowders, which can be placed in the mixture in an equal amount. However,in other instances, a greater or lesser amount of one of the fine orcoarse silicon carbide powder can be used. In one particular embodiment,the mixture includes between about 30 wt % and about 50 wt % of each ofthe fine and coarse silicon carbide powders.

Certain other additive powder materials can be provided in the mixture.The additives can include powder components having a composition such assilicon, nitrides, carbides, oxides, borides, oxynitrides, oxyborides,and a combination thereof. Generally, the additives are present in minoramounts, such as less than about 25 wt %, not greater than about 20 wt%, not greater than about 15 wt %, not greater than about 10 wt %, oreven not greater than about 5 wt % of the total weight of the mixture.For example, particular compositions incorporating some content ofsilicon can include at least about 10 wt %, such as at least about 12 wt%, at least about 14 wt %, or even at least about 16 wt % silicon.Still, in such embodiments, the amount of silicon can be not greaterthan about 25 wt %, not greater than about 22 wt %, not greater thanabout 20 wt %, or even not greater than about 18 wt %.

In reference to still other mixtures used in the formation ofnitride-bonded silicon carbide bodies, use of materials such as oxides,oxynitrides, and nitrides, can be limited. For example, in particularinstances, the presence of such materials may be not greater than about12 wt %, such as not greater than about 10 wt %, not greater than about8 wt %, or even not greater than about 5 wt %.

In one particular embodiment, the additives include materials such asaluminum oxide, iron oxide, and a combination thereof. For example, themixture can include approximately 5 wt % alumina powder. Moreover,certain mixtures can include a minor amount of iron oxide, such asapproximately 0.5 wt %. Furthermore, the mixture may include somecontent of silicon powder, generally on the order of 1 wt % to about 10wt %.

After suitably forming the mixture at step 101, the process can continueat step 102 by shaping the mixture into a green body. It will beappreciated that reference to a green body is reference to anun-sintered body that has not undergone heat treatment to densify thebody. The shaping process can include various operations includingcasting, molding, pressing, extruding, and a combination thereof. In oneparticular instance, the process of shaping the mixture into a greenbody includes a slip casting process. For a detailed description oftechniques for forming a ceramic body, attention is drawn to U.S. Pat.No. 4,990,469, incorporated herein by reference. Other suitable shapingmethods can include drip casting, pressing, pressure casting, extrusion,and other techniques.

After shaping the mixture into a green body at step 102 the process cancontinue at step 103 by firing the green body to form a sintered ceramicbody. Firing can be conducted in a chamber at a particular firingtemperature, such as at least about 800° C. In other instances, thefiring temperature can be greater, such as at least about 900° C., atleast about 1000° C., or even at least about 1050° C. In accordance withanother embodiment, the firing temperature can be not greater than about2000° C., such as not greater than about 1800° C., not greater thanabout 1500° C., or even not greater than about 1480° C. It will beappreciated that firing can be conducted at a firing temperature withina range between any of the minimum and maximum values noted above.

Firing may be conducted for a duration of at least about 1 hour. Inother instances, the process of firing can be longer, such that thefiring duration can be at least about 10 hours, such as at least about25 hours, at least about 30 hours, at least about 40 hours, or even atleast about 45 hours. In particular instances, the firing process canhave a duration of firing within a range between about 10 hours andabout 80 hours, such as between about 20 hours and about 65 hours. Itwill be appreciated that firing is generally considered the time betweenthe increase in temperature as the green body is placed in the chamberto a time before the temperature is reduced in the housing and coolingis undertaken.

Firing may be conducted in a controlled atmosphere. In accordance withan embodiment, the atmosphere can be a reducing atmosphere. Moreparticularly, the atmosphere during firing can include nitrogen. Incertain processes, the atmosphere during firing can consist essentiallyof nitrogen. Such atmosphere may be effective in reacting siliconcontained in the body with the nitrogen in the atmosphere, causing theformation of the silicon nitride as a secondary phase that bonds theprimary silicon carbide phase and forms a nitride-bonded silicon carbidebody.

Notably, during the firing process, certain fibrous materials may beformed on the ceramic body. The fibrous material may include a carbide,nitride, boride, or a combination thereof. In particular instances, thefibrous material includes silicon nitride fibers which are formed as aresult of the firing process. Such fibers can have a needle-like shape,extend over substantially all of the major exterior surfaces of thebody, and be microscopic. In some cases, the fibers may negativelyaffect post-sintering processes, particularly those directed toformation of a coating layer on the body.

After firing the green body to form a sintered ceramic body at step 103,the process can continue at step 104, by treating the ceramic body. Inaccordance with an embodiment, the process of treating the ceramic bodycan include inducing a chemical reaction that facilitates removal of aportion of the ceramic body through the chemical reaction between areactant material within the chamber and a portion of the ceramic body.Notably, the process of treating the ceramic body may be conducted inthe same chamber as firing is conducted, such that the ceramic body doesnot need to be removed after firing and placed in a different chamber.Accordingly, the treating process includes an in-situ chemical reactionto remove a portion of the ceramic body, which may be formed during thefiring process.

Treating the ceramic body can include changing the atmosphere within thechamber after firing. Accordingly, the atmosphere during treating can bedifferent than the atmosphere utilized during firing. It will beappreciated that reference to a different atmosphere is reference to twoatmospheres, wherein one of the atmospheres differs from the otheratmosphere by at least one elemental component, which can be in the formof a free element, composition, compound, and/or complex.

In accordance with an embodiment, treating the ceramic body includesutilizing an oxidizing material within the atmosphere to facilitateremoval of a portion of the ceramic body through a chemical reactionthat takes place between the oxidizing material and the ceramic body.The chemical reaction undertaken during treating of the ceramic body canfacilitate removing material from an exterior surface of the ceramicbody. In more particular instances, the reaction can facilitate removalof material from pores that extend into the interior volume of theceramic body. As such, the process of treating the ceramic body canfacilitate removal of the fibrous material from the exterior surface ofthe body, and pores extending into the interior volume of the bodyconnected to the exterior surface.

In accordance with an embodiment, the oxidizing material may be agaseous reactant material suitable for oxidizing a portion of theceramic body. For example, the oxidizing material can include oxygen.One process can include an oxidizing material in the form of a compoundincluding carbon. According to a particular embodiment, the oxidizingmaterial can include carbon dioxide, and more particularly, theoxidizing material may consist essentially of carbon dioxide.

In certain instances, the process of treating the ceramic body caninclude a chemical reaction defining a phase transition of one or morechemical components involved in the chemical reaction. That is, forexample, a portion of the body can be removed through a phasetransition, such that a portion of the body transforms phases from asolid phase to a gas phase. In accordance with one particular reaction,treating of the ceramic body may be conducted such that an oxidizingmaterial is introduced into the chamber, wherein the oxidizing materialreacts with a portion of the ceramic body, which as a result, transformsthe portion of the ceramic body from a solid phase material to a gasphase material.

The chemical reaction between the oxidizing material and a portion ofthe ceramic body can form a reaction product that may include an oxidematerial. For example, the oxide material can be a chemical compoundincluding silicon. For instance, the oxide material that is a reactionproduct of the chemical reaction between the oxidizing material and theportion of the ceramic body can include silicon monoxide, and moreparticularly, may consist essentially of silicon monoxide.

Another, additional oxide material, separate from the one noted above,may be formed as a reaction product from treating the ceramic body. Suchan oxide material can be in the form of a gas. More particularly, thereaction product can be a chemical composition including carbon. Incertain instances, a reaction product of carbon monoxide can be formedas a result of the reaction between the ceramic body and the oxidizingmaterial.

A reaction product comprising a nitrogen material may also be formed asa result of the reaction between a portion of the ceramic body and thegaseous reactant material. In certain instances, a reaction product ofnitrogen gas may be formed, and more particularly, a reaction productconsisting essentially of nitrogen gas can be the nitrogen reactionproduct.

In accordance with one particular embodiment, the reaction between aportion of the ceramic body comprising the fibrous silicon nitridematerial and a gaseous reactant material in the form of an oxidizingmaterial can result in oxidation of the silicon nitride fibers,represented by the following chemical formula:

Si₃N₄+3CO₂→3SiO+3CO+2N₂

The process of treating the ceramic body may be conducted at aparticular temperature to facilitate the chemical reaction. In fact, ithas been noted that a certain minimum threshold temperature may beutilized to drive the reaction, and below such a temperature, thereaction may not necessarily occur. For example, the process of treatingthe ceramic body can be conducted at a reaction temperature that is atleast about 800° C. In other instances, the reaction temperature can beat least about 900° C., such as at least about 950° C., at least about1000° C., at least about 1100° C., or even at least about 1200° C. Inother instances, the process of treating the ceramic body may beconducted at a reaction temperature that is not greater than about 2000°C., such as not greater than about 1800° C., not greater than about1500° C., or even not greater than about 1300° C. It will be appreciatedthat the reaction temperature can be within a range between any of theminimum and maximum value recited above.

Notably, the oxidizing material can be flowed through the processingchamber at a particular rate to facilitate the reaction. In fact, acertain flow rate may be utilized to ensure the chemical reactionbetween the portion of the ceramic body and the oxidizing materialoccurs. In one embodiment, the oxidizing material can be flowed into thechamber at a flow rate of at least 1 standard cubic foot per hour (scfh)or 0.028 cubic meters per hour. In still other embodiments, the processof treating the ceramic body can include flow of an oxidizing materialthrough the chamber at a flow rate of at least about 2 scfh (0.057 cubicmeters per hour), such as at least about 3 scfh (0.085 cubic meters perhour), at least about 4 scfh (0.11 cubic meters per hour), or even atleast about 5 scfh (0.14 cubic meters per hour). Still, the flow rate ofthe oxidizing material into the chamber during the process of treatingthe ceramic body can be not greater than about 200 scfh (5.7 cubicmeters per hour), such as not greater than about 175 scfh (5.0 cubicmeters per hour), or even not greater than about 150 scfh (4.2 cubicmeters per hour). It will be appreciated that the flow rate of oxidizingmaterial through the chamber during treating of the ceramic body can bewithin a range between any of the minimum and maximum values notedabove.

A certain amount of the atmosphere of the chamber during treating maycontain the gaseous reactant material. The atmosphere of the chamberduring treating can include at least about 50 vol % of the gaseousreactant material for the total volume of the chamber to facilitate thereaction. In more particular embodiments, at least about 60 vol %, suchas at least about 70 vol %, at least about 80 vol %, at least about 90vol %, or even essentially the entire volume of the chamber can befilled with the gaseous reactant material during the process oftreating.

Treating can be conducted for a treatment duration of at least about 10minutes. In other processes, the treatment duration can be longer, suchas at least about 30 minutes, at least about 45 minutes, at least about60 minutes, at least about 90 minutes, or at least about 120 minutes. Incertain instances, the treatment duration can be not greater than about24 hours, such as not greater than about 18 hours, not greater thanabout 12 hours, or even not greater than about 8 hours. It will beappreciated that the treatment duration can be within a range betweenany of the minimum and maximum values noted above.

In accordance with an embodiment, the process of treating the ceramicbody can further include a cooling process, wherein the temperaturewithin the chamber is decreased after firing to initiate the process oftreating the ceramic body. Notably, the cooling process can becontrolled such that the temperature is properly controlled tofacilitate treating of the ceramic body. In one instance, thetemperature is reduced after firing to initiate a cooling process, whilemaintaining the temperature above a particular threshold temperature tofacilitate a reaction during the treating process. Upon cooling, theatmosphere within the chamber can be changed from the firing atmosphereto the treating atmosphere to initiate the treating process.

The resulting ceramic body can be a nitride-bonded silicon carbide body.In accordance with one embodiment, the ceramic body can have a Knoophardness of at least about 1500 kg/mm². In other instances, the Knoophardness can be greater, such as at least about 1800 kg/mm², such as atleast about 2000 kg/mm², or even at least about 2500 kg/mm². In certaininstances, the ceramic body can have a Knoop hardness of less than about4000 kg/mm², such as less than about 3500 kg/mm², even less than about3000 kg/mm², or even less than about 2700 kg/mm².

In accordance with another embodiment, the ceramic body can have acorrosion resistance, as measured by weight loss in 53% hydrochloricacid, not greater than 15 mg/cm² yr. In other instances, the corrosionresistance is better, having a weight loss that is not greater thanabout 12 mg/cm² yr, not greater than about 10 mg/cm² yr. Still, theweight loss can be at least 5 mg/cm² yr. It will be appreciated that thecorrosion resistance can be within a range between any of the minimumand maximum values noted herein.

After treating, the nitride-bonded silicon carbide ceramic body can havea porosity of less than about 25 vol % of the total volume of the body.In other instances, the porosity of the ceramic body can be less, suchas not greater than about 20 vol %, not greater than about 18 vol %, oreven not greater than about 15 vol % of the total volume of the ceramicbody. It will be appreciated that the porosity may be at least about 1vol %, such as at least about 2 vol %, at least about 3 vol %, or evenat least about 5 vol % of the total volume of the ceramic body. It willbe appreciated that the total volume of porosity within the ceramic bodycan be within a range between any of the minimum and maximum valuesnoted above.

Furthermore, a fraction of the porosity present within the ceramic bodycan be open porosity, which may be defined by a network ofinterconnected pores within the body that intersect the exteriorsurface. The nitride-bonded silicon carbide ceramic body generallycontains at least about 1 vol %, such as at least about 5 vol %, atleast about 8 vol %, or even at least about 10 vol % open porosity forthe total volume of porosity within the body.

In accordance with another embodiment, the ceramic body can be formedsuch that it has a density that is at least about 75% of theoreticaldensity. In other instances, the ceramic body can have a density that isat least about 80%, such as at least about 90%, at least about 92%, oreven at least about 95% of theoretical density.

As further illustrated in FIG. 1, the process of forming a ceramic bodycan further include an optional step 105 which includes coating of theceramic body. Coating of the ceramic body can include formation of acoating layer that overlies the exterior surface of the body. Thecoating may overlie essentially the entire exterior surface of the bodysuch that the ceramic body is encapsulated by the coating layer. Inaccordance with an embodiment, the coating layer can include an oxidematerial. More particularly, the coating layer can include an aluminaoxide material and/or a mullite material, which is an alumina silicatematerial (3Al₂O₃.2SIO₂). In more particular instances, the coating layercan include an amorphous phase. In still other instances, the coatinglayer can include a crystalline phase. Certain coating layers caninclude a combination of amorphous phase and crystalline phase whereinthe crystalline phase may be mainly in the form of needle-shapedcrystals comprising the alumina silicate material.

The process of forming the coating layer can be affected by spraying,dipping, brushing, and the like. For example, a spraying process caninclude an air sprayer to achieve a thin, uniform coating on the surfaceof the ceramic body. In other instances more complex shapes of ceramicbody may include a submersion approach, such as dipping, wherein theceramic body is placed in a slurry containing a mixture of the materialcomponents suitable for forming the coating layer.

After sufficiently coating the ceramic body with the desired material,the coating process can further include a heat treatment. Heat treatmentcan be conducted in a particular atmosphere, such as an oxidizingatmosphere, which can include ambient air. The heat treatment processcan be conducted at elevated temperatures, such as on the order of atleast about 1000° C., at least about 1100° C., or even at least about1200° C. In such an instance, the material sprayed or otherwise coatedon the nitride-bonded silicon carbide body can be oxidized to form thecoating layer. Further aspects of the process of forming the coatinglayer and characteristics of the coating layer are set forth in U.S.Pat. No. 7,732,026 which is incorporated in its entirety by reference.

In particular reference to the nitrogen-bonded silicon carbide material(i.e., without an optional coating layer), the process of treating theceramic body can facilitate the removal of fibrous material from theexterior surface of the body as well as pores within the body that mayextend into the interior volume of the body. Such bodies are distinctfrom conventional nitrogen-bonded silicon carbide bodies, sinceconventional techniques for removing such fibrous growths on the bodyinclude mechanical abrading techniques including, for example, sandblasting techniques, which simply remove the fibers from the exteriorsurface of the body without removing the fibers from crevices and poreson the surface, and furthermore, can actually roughen the exteriorsurface of the body. Accordingly, the ceramic body of the embodimentsherein can be characterized by smooth, non-fibrous surfaces when theexterior surface is viewed at magnifications of at least 1000× for atleast two random locations across the exterior surface of the body.

In particular, the ceramic bodies of the embodiments herein arecharacterized by a non-fibrous exterior surface having not greater than10 fibers per hundred square microns when viewed at a magnification ofat least 1000× at two random locations on the exterior surface of theceramic body. In fact, in other embodiments, the existence of fibers iseven more scarce, such that the exterior surface of the ceramic body ischaracterized by having not greater than 5 fibers per 100 squaremicrons, not greater than 1 fiber per 100 square microns, not greaterthan about 1 fiber per 500 square microns, or even not greater than 1fiber per 1000 square microns when at least 2 random locations on theexterior surface of the body are viewed at a magnification of at least1000×.

Example

A nitride-bonded silicon carbide body is formed according to embodimentsherein by initially combining the components provided in Table 1 belowin a slurry. The sample of Example 1, formed according to theembodiments herein, is designated sample S1.

TABLE 1 6521-100F SILICON CARBIDE GREEN 35.5 wt % 7662-30 SILICONCARBIDE GREEN 33.3 wt % C-8774 IRON OX #222 BAYER 0.44 wt % WD DEIONIZEDWATER 11.01 wt %  C-8770 A-3000FL CALCINED ALU 4.44 wt % C-8773 ELKEM SI0.30% FE 15.07 wt % 

After forming the initial mixture in the form of a slurry, the mixtureis slip cast to form a green body. The green body is placed in a firingchamber wherein the temperature is increased to 700° C. at 100° C./hrand nitrogen gas is introduced into the chamber. Thereafter, thetemperature is increased to approximately 1350° C. while nitrogen gascontinues to flow. The temperature is increased to 1440° C. and issoaked for 6 hours in a nitrogen gas atmosphere. After 6 hours of firingat 1440° C., the nitrogen gas atmosphere is purged from the firingchamber and CO₂ is introduced as an oxidizing material within thechamber to react with a portion the fired silicon carbide body. CO₂ isflowed through the chamber at 4 scfh for approximately 5 hours while thetemperature in the chamber is reduced and cooling of the ceramic body isinitiated. After 5 hours of flowing CO₂ into the chamber, the atmosphereis again changed such that ambient air is flowed into the chamber whilethe ceramic body cools to room temperature. FIG. 2 includes a firingschedule demonstrating the temperature of the chamber during the processof forming the ceramic body of Example 1.

A conventional sample (C1) comprising nitride-bonded silicon carbide isformed according to a conventional process that utilizes a similarprocess as noted above with regard to sample S1; however, no treatingprocess is conducted. The firing process to form sample C1 is the sameas sample S1. However, after firing, no CO₂ is introduced into thechamber. After cooling to room temperature, silicon nitride fibers areevident on the sample C1. No silicon nitride fibers are observable onthe sample S1.

Sample C1 is sandblasted using 10-40 lbs of pressure and 24 mesh sizegrit of brown, fused alumina.

FIGS. 3 and 4 include magnified images of a portion of the ceramic bodyof sample S1 formed according to the embodiments herein. FIGS. 3 and 4include magnified images of pores on the exterior surface of the SampleS1. As clearly shown, sample S1 is essentially free of fibrous materialon the exterior surface, even when observed at magnifications of 500×and 1000×.

By comparison, a portion of the conventional sample is illustrated inthe magnified images of FIGS. 5 and 6. Clearly, as shown in FIGS. 5 and6, the conventional sample has fibers extending over the surface andobstructing the crevices and pores on the exterior surface of theceramic body. Considering that the viewed area in each of FIGS. 5 and 6is greater than 1000 square microns, clearly the concentration of fibersof sample C1 is significantly greater than that of sample S1, and moreparticularly, significantly greater than 10 fibers per hundred squaremicrons.

The embodiments herein are directed to nitride-bonded silicon carbidearticles and methods of forming such articles. The embodiments hereinare directed to a combination of processing techniques configured tofacilitate the formation of nitride-bonded silicon carbide bodies usinga more efficient, streamlined process. Such features include a treatingprocess, wherein a chemical reaction occurs between a portion of thesilicon carbide body and a gaseous reactant material introduced into thefiring chamber under particular conditions (e.g., temperature, pressure,duration, flow rate, etc.). Accordingly, portions of the body areremoved in-situ, alleviating the need for future, time-consumingprocessing, which would otherwise be necessary to remove the undesirableportions.

Furthermore, the result of the unique combination of processingparameters results in an ceramic article having unique, identifiablefeatures as compared to nitride-bonded silicon carbide bodies formedthrough conventional processing pathways. Such features include, but arenot limited to, particularly low concentrations of fibrous material onthe exterior surface, and mechanical features. The embodiments provide acombination of features, which can be combined in various manners todescribe and define the refractory bodies of the embodiments. Thedescription is not intended to set forth a hierarchy of features, butdifferent features that can be combined in one or more manners to definethe invention.

In the foregoing, reference to specific embodiments and the connectionsof certain components is illustrative. It will be appreciated thatreference to components as being coupled or connected is intended todisclose either direct connection between said components or indirectconnection through one or more intervening components, as will beappreciated, to carry out the methods as discussed herein. As such, theabove-disclosed subject matter is to be considered illustrative, and notrestrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments, which fall withinthe true scope of the present invention. Thus, to the maximum extentallowed by law, the scope of the present invention is to be determinedby the broadest permissible interpretation of the following claims andtheir equivalents, and shall not be restricted or limited by theforegoing detailed description.

The disclosure is submitted with the understanding that it will not beused to interpret or limit the scope or meaning of the claims. Inaddition, in the foregoing disclosure, various features may be groupedtogether or described in a single embodiment for the purpose ofstreamlining the disclosure. This disclosure is not to be interpreted asreflecting an intention that the embodiments herein limit the featuresprovided in the claims, and moreover, any of the features describedherein can be combined together to describe the inventive subjectmatter. Still, inventive subject matter may be directed to less than allfeatures of any of the disclosed embodiments.

1. A method of forming a ceramic article comprising: providing a ceramicbody comprising silicon carbide; and treating the ceramic body in anatmosphere comprising an oxidizing material to remove a portion of theceramic body through a chemical reaction between a portion of theceramic body and the oxidizing material.
 2. The method of claim 1,wherein the oxidizing material comprises oxygen.
 3. The method of claim1, wherein the oxidizing material comprises carbon.
 4. The method ofclaim 3, wherein the oxidizing material comprises carbon dioxide.
 5. Themethod of claim 1, wherein the oxidizing material comprises a gaseousmaterial.
 6. The method of claim 5, wherein treating comprises providingthe oxidizing material into a chamber containing the ceramic body at aflow rate of at least about 1 standard cubic foot per hour (scfh) (0.028cubic meters per hour).
 7. The method of claim 6, wherein duringtreating the oxidizing material is provided into the chamber at a flowrate of at least about 2 scfh (0.057 cubic meters per hour).
 8. Themethod of claim 7, wherein during treating the oxidizing material isprovided into the chamber at a flow rate of at least about 3 scfh (0.085cubic meters per hour).
 9. The method of claim 8, wherein duringtreating the oxidizing material is provided into the chamber at a flowrate of at least about 4 scfh (0.11 cubic meters per hour).
 10. Themethod of claim 6, wherein during treating the oxidizing material isprovided into the chamber at a flow rate of not greater than about 200scfh (5.7 cubic meters per hour).
 11. The method of claim 1, wherein theoxidizing material comprises carbon dioxide.
 12. The method of claim 11,wherein the oxidizing material consists essentially of carbon dioxide.13. The method of claim 1, wherein treating the ceramic body comprisesremoving material from an exterior surface of the ceramic body.
 14. Themethod of claim 1, wherein treating the ceramic body comprises removingmaterial from pores extending into the ceramic body.
 15. The method ofclaim 1, wherein treating the ceramic body comprises removing fibrousmaterial from the ceramic body.
 16. The method of claim 1, wherein thechemical reaction includes a phase transition of the portion of theceramic body removed.
 17. The method of claim 16, wherein the phasetransition includes a change of solid material to gaseous material. 18.The method of claim 1, wherein the chemical reaction includes oxidationof a portion of the ceramic body by the oxidizing material to create areaction product including an oxide material.
 19. The method of claim18, wherein the oxide material comprises silicon.
 20. The method ofclaim 19, wherein the oxide material consists essentially of siliconmonoxide.
 21. The method of claim 18, wherein the oxide materialcomprises a gas.
 22. The method of claim 18, wherein the oxide materialcomprises carbon.
 23. The method of claim 22, wherein the oxide materialcomprises carbon monoxide.
 24. The method of claim 1, wherein thechemical reaction includes oxidation of a portion of the ceramic body bythe oxidizing material to create a reaction product including a nitrogenmaterial.
 25. The method of claim 24, wherein the nitrogen materialcomprises a gas.
 26. The method of claim 25, wherein the nitrogenmaterial consists essentially of nitrogen gas.
 27. The method of claim1, wherein treating includes operating at a reaction temperature of atleast about 800° C.
 28. The method of claim 27, wherein the reactiontemperature is at least about 900° C.
 29. The method of claim 28,wherein the reaction temperature is at least about 950° C.
 30. Themethod of claim 29, wherein the reaction temperature is at least about1000° C.
 31. The method of claim 1, wherein treating includes operatingat a reaction temperature of not greater than about 2000° C.
 32. Themethod of claim 31, wherein the reaction temperature is not greater thanabout 1800° C.
 33. The method of claim 32, wherein the reactiontemperature is not greater than about 1500° C.
 34. The method of claim33, wherein the reaction temperature is not greater than about 1300° C.35. A method of forming a ceramic article comprising: providing aceramic body comprising a fibrous material overlying an exterior surfaceof the ceramic body; and treating the ceramic body with a gaseousreactant material to remove the fibrous material from the ceramic bodythrough a chemical reaction between the gaseous reactant material andthe fibrous material.
 36. The method of claim 35, wherein the gaseousreactant material comprises an oxidizing material.
 37. The method ofclaim 36, wherein the oxidizing material comprises carbon dioxide. 38.The method of claim 35, wherein treating comprises providing the gaseousreactant material into a chamber containing the ceramic body at a flowrate of at least about 1 standard cubic foot per hour (scfh) (0.028cubic meters per hour).
 39. The method of claim 35, wherein treating theceramic body comprises removing the fibrous material from pores withinthe ceramic body.
 40. The method of claim 35, wherein the chemicalreaction includes a phase transition of the portion of the fibrousmaterial from a solid phase material to a gas phase material.
 41. Themethod of claim 35, wherein the chemical reaction includes oxidation ofthe fibrous material to form a reaction product comprising an oxidematerial.
 42. The method of claim 41, wherein the oxide materialcomprises silicon monoxide.
 43. The method of claim 41, wherein theoxide material comprises carbon monoxide.
 44. The method of claim 35,wherein the chemical reaction includes oxidation of the fibrous materialto form a reaction product comprising a nitrogen material.
 45. Themethod of claim 44, wherein the nitrogen material consists essentiallyof nitrogen gas.
 46. The method of claim 35, wherein treating includesoperating at a reaction temperature of at least about 800° C.
 47. Themethod of claim 46, wherein treating includes operating at a reactiontemperature of not greater than about 2000° C.
 48. The method of claim35, further comprising firing the ceramic body prior to treating. 49.The method of claim 48, wherein firing is conducted at a firingtemperature of at least about 800° C.
 50. The method of claim 49,wherein firing is conducted at a firing temperature of at least about900° C.
 51. The method of claim 50, wherein firing is conducted at afiring temperature of at least about 1000° C.
 52. The method of claim48, wherein firing is conducted at a firing temperature of not greaterthan about 2000° C.
 53. The method of claim 52, wherein firing isconducted at a firing temperature of not greater than about 1800° C. 54.The method of claim 53, wherein firing is conducted at a firingtemperature of not greater than about 1500° C.
 55. The method of claim48, wherein firing is conducted for a firing duration of at least about1 hour.
 56. The method of claim 55, wherein firing is conducted for afiring duration of at least about 10 hours.
 57. The method of claim 35,wherein treating comprises cooling the ceramic body after conducting afiring operation.
 58. The method of claim 57, wherein cooling comprisesreducing a temperature of a chamber containing the ceramic body from afiring temperature
 59. The method of claim 35, wherein treating isconducted for a treatment duration of at least about 10 minutes.
 60. Themethod of claim 59, wherein treating is conducted for a treatmentduration of at least about 30 minutes.
 61. The method of claim 60,wherein treating is conducted for a treatment duration of at least about60 minutes.
 62. The method of claim 59, wherein treating is conductedfor a treatment duration of not greater than about 24 hours.
 63. Themethod of claim 62, wherein treating is conducted for a treatmentduration of not greater than about 12 hours.
 64. The method of claim 63,wherein treating is conducted for a treatment duration of not greaterthan about 8 hours.
 65. A method of forming a ceramic articlecomprising: firing a ceramic body comprising silicon carbide in a firstatmosphere; and treating the ceramic body in a second atmosphere afterfiring, wherein the second atmosphere is different than the firstatmosphere and comprises a reactant material that chemically reacts withthe ceramic body and removes a portion of the ceramic body.
 66. Aceramic article comprising: a body comprising nitride-bonded siliconcarbide, wherein the body comprises pores at an exterior surface and amajority of the pores are defined by smooth, non-fibrous surfaces whenviewed at a magnification of at least 1000× for at least 2 randomlocations across the exterior surface of the body.
 67. The ceramicarticle of claim 66, wherein the body comprises an open porosity withinthe body of at least about 2 vol % for a total amount of porosity withinthe body.
 68. The ceramic article of claim 66, wherein the bodycomprises a density of at least about 75% of theoretical density. 69.The ceramic article of claim 66, wherein the body consists essentiallyof nitride-bonded silicon carbide.
 70. The ceramic article of claim 66,wherein the body comprises a coating layer overlying the body.
 71. Theceramic article of claim 70, wherein the coating layer comprises anoxide.
 72. The ceramic article of claim 70, wherein the coating layercomprises an amorphous phase.
 73. A ceramic article comprising: a bodycomprising nitrogen-bonded silicon carbide having a non-fibrous exteriorsurface, wherein a non-fibrous exterior surface is defined by a surfacehaving not greater than 10 fibers per 100 square microns at amagnification of at least 1000× for at least 2 random locations acrossthe exterior surface of the body.
 74. The ceramic article of claim 73,wherein the exterior surface is defined by a surface having not greaterthan 5 fibers per 100 square microns at a magnification of at least1000× for at least 2 random locations across the exterior surface of thebody.
 75. The ceramic article of claim 73, wherein the exterior surfaceis defined by a surface having not greater than 1 fiber per 100 squaremicrons at a magnification of at least 1000× for at least 2 randomlocations across the exterior surface of the body.